This project will investigate the effects of the ovarian hormones, estrogen and progesterone, on lysosomal enzyme activities in the rat heart by correlated biochemical and morphological methods. Specific activities of five representative lysosomal acid hydrolases in the heart will be assayed colorimetrically or fluorometrically at intervals after ovariectomy and after subsequent administration of estrogen and progesterone. The stability of the cardiac lysosomal membrane will be assessed by measuring both free and nonsedimentable acid hydrolase activities. Morphological and histochemical studies will use morphometric methods to demonstrate whether increases in the number or in the size of lysosomal structures are found in the cardiac muscle, the cardiac vasculature and/or the interstitial cells, and if these increases correspond to ovarian hormone-mediated increases in acid hydrolase activities. Since lysosomes may contribute to myocardial ischemic damage resulting from coronary artery ligation, estrogen and/or progesterone administration could reduce ischemic damage if the ovarian hormones can be shown to increase the stability of the cardiac lysosomal membranes or reduce cardiac acid hydrolase activities.